The invention relates to a bottle cover and, more particularly, to the structure of a negative-pressure-resistible leakage-proof bottle cover.
The structure of a common bottle cover is shown in FIGS. 1 and 2. A plurality of threads are formed at an inner edge of a cover body serving as a female connector to match those on a bottle mouth serving as a male connector for a firm engagement. In the cover body, an anti-tampering ring is provided at a lower position and a leakage-proof gasket is provided on an inner top face.
The leakage-proof gasket is circular and formed from an elastomer that is processed from thermoplastic materials. It is designed thicker at the circumference than at the center. The circumferential portion is bent downward and is slightly extended and converged to form a single circular edge to deform at protrusions on an inner wall of the bottle body for positioning when the leakage-proof gasket is pressed onto the inner top face of the bottle cover.
This known leakage-proof gasket has a disadvantage in that the gasket is thickened at its circumference, and since both the contact faces of the gasket and the top edge of a bottle mouth are planer, a relatively larger torque force will be required for sealing the bottle mouth. It is rather a inconvenient, or even harmful to a user. In case a bottle filled with a beverage at 85.degree. C. or higher becomes cold, a negative pressure will be created in the bottle, so that air will infiltrate into the bottle. This is why a common bottle cover cannot withstand the effect of negative-pressure.
The integral molded anti-tampering ring located around the open end of the cover body with a relatively smaller inner diameter than that of the opening, connects to the cover body via intermittently spaced gaps and strips. Several choke fins are round-set at an inner side of the anti-tampering ring for clutching at the bottom edge of threads formed at an outer side of the bottle mouth. The thickness of the anti-tampering ring is about equal to that of the cover body, and, when sealing, the ring is subjected to downward and outward pressures from the cover body and threads at the bottle mouth. It cannot pass smoothly over the threaded section and may become deformed and torn. The intermittently spaced strips are liable to be broken.